Elimination of chemicals

Saturation kinetics are also called zero-order kinetics or Michaelis-Menten kinetics. The Michaelis-Menten equation is mainly used to characterize the interactions of enzymes and substrates, but it is also widely applied to characterize the elimination of chemical compounds from the body. The substrate concentration that produces half-maximal velocity of an enzymatic reaction, termed value or Michaelis constant, can be determined experimentally by graphing r/, as a function of substrate concentration, [S]. 

In a classic study, Neely, Branson and Blau (13) showed that the rate of uptake and elimination of chemicals in trout was related to the chemical s octanol/water partition coefficient. Just as a drop of octanol would equilibrate with one million times the concentration of some PCBs as the water which surrounded it, so... 

Factors affecting absorption, distribution, binding, metabolism, and elimination of chemicals... 

Membrane transporter proteins (MDR or ABC transporter proteins) such as p-glycoprotein are crucially important in the process of excretion and also in absorption and distribution and elimination of chemicals from cells. These transport organic anions or cations and neutral compounds across membranes, pump unwanted chemicals out of cells such as in gut, placenta, and brain, transport chemicals into bile from liver cells, and facilitate excretion from the kidney. 

Landrum et al. (1992) developed a kinetic bioaccumulation model for PAHs in the amphipod Diporeia, employing first-order kinetic rate constants for uptake of dissolved chemical from the overlying water, uptake by ingestion of sediment, and elimination of chemical via the gills and feces. In this model, diet is restricted to sediment, and chemical metabolism is considered negligable. The model and its parameters, as Table 9.3 summarizes, treat steady-state and time-variable conditions. Empirically derived regression equations (Landrum and Poore, 1988 and Landrum, 1989) are used to estimate the uptake and elimination rate constants. A field study in Lake Michigan revealed substantial differences between predicted and observed concentrations of PAHs in the amphipod Diporeia. Until more robust kinetic rate constant data are available for a variety of benthic invertebrates and chemicals, this model is unlikely to provide accurate estimates of chemical concentrations in benthic invertebrates under field conditions. 

Host-mediated assay, m the host-mediated assay, target cells cure inoculated into an animal that receives the chemical treatment. The assay can be performed only with cell lines that do not kill and cure not killed by the host. Several chemicals—including AF-2, EMS, DMN, DEN, and MNNG—have been tested in this assay system. These chemicals induce mutations in the direct test or in cell-or microsome-mediated assays. Such studies may be useful in understanding responses—including tissue distribution, activation, detoxification, and elimination of chemicals— in whole animals. 

Excretion Elimination of chemicals from the body. Chemicals may be excreted through feces, urine, exhaled breath, etc. 

Complete and permanent chemical disarmament, once a distant goal, is now being implemented daily around the world by the member states of the Organisation for the Prohibition of Chemical Weapons (OPCW). This multilateral and complex task inspired an international symposium held at the United Nations University in 2003, titled Towards the Elimination of Chemical Weapons The Roles of the OPCW and Japan , and serves as the basis for the invaluable research summarized in this text. 

Active transport is of limited importance for absorption of chemicals it plays an important role, however, in the elimination of chemicals by the liver and the kidneys. 

Excretion is the process by which chemicals are eliminated from the body. When chemicals gain access to the body, they usually do so as lipid-soluble molecules. In order to be eliminated, most of them must first undergo biotransformation to become more water soluble and, consequently, more easily excreted. Biotransformation and excretion are therefore the main processes involved in the elimination of chemicals. 

All chemicals absorbed in the gastrointestinal tract first reach the liver, where they normally undergo biotransformation to new, more water-soluble molecules (metabolites). Some of these will eventually be excreted in the bile. Thus, in addition to playing an important role in the digestion and intestinal absorption of fats, bile is also involved in the elimination of chemicals from the body. 

Not a comprehensive list for example, metabolism can occur in the GI tract, and elimination of chemicals can occur through hair. 

U.S. Army. 2005. System Requirements Document for the Large Item Transportable Access and Neutralization System, October. Aberdeen Proving Ground, Md. Program Manager for the Elimination of Chemical Weapons. 

Hepatic and intestinal induction of drug transporters is well documented however, data are sparse in other tissues. It is especially challenging to analyze the induction of drug transporters in kidney and blood-brain barrier, as these tissues play important roles in the elimination of chemicals and in controlling the CNS accessibility of drugs, respectively. 

The conditioning and control of indoor environments is an ever increasing problem. Lately this does not only include the traditional control of temperature and moisture but also the elimination of contaminants and odors from the atmosphere. Particulates, including organic matter, such as mold, germs, and viruses, can be captured and retained by sometimes electrically assisted ultrafiltration. Cartridges are either discarded or cleaned/reactivated. For the elimination of chemicals and odors, absorption, adsorption, and chemical reactions with air purification media are required. 

Fig. 28. (a) The basic BABA pulse sequence over one rotation period, (b) Supercycle for the elimination of chemical shielding contributions over two rotation periods. ... 

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